HP Plasma CPTOH-0603- Picture goes blank after a few minutes

[mh321]

Hello, I have a HP cptoh-0603 plasma TV that I want to try to repair. When you plug the TV in, it turns on normally, there is picture, but after about 5 minutes the screen flickers for about 1 second and then goes blank. The power button LED still shows the TV as being powered on. Once the screen goes out, the only way to get the picture back is to unplug the TV for 10 seconds, and plug it back in.

I am going to try opening the TV up this evening, as I got it just yesterday, but I am wondering what parts might be causing this, and how to determine what needs fixing.

Thanks

[tom66]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

When the picture goes out, can you see faint screen glow (may need a dark room) and does sound continue?

[mh321]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

With the room's lights off, and blue screen mode turned off to see the static on ch3, before the picture went out, the screen got very white for 1.5s. After the white stopped, I was able to see a few very dim flickering white pixels similar to the ch3 static. Powering the TV on or off without pulling the plug makes those dim pixels/static brighter for an instant.

The TV doesn't have any speakers, and I haven't connected it to a stereo yet, but do these results give some good clues to what might be wrong?

Thanks

[mh321]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

Any ideas?

[mh321]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

The boards are made by LG, if that helps

[capkid]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

A common failure in these TVs when they exhibit picture issues is the Y-Sustain or the Z-Sustain. However, the power supply (PSU) is also known to fail, and it sounds like that could be your issue here. Do you have a digital multimeter? If so, monitor these voltages when the picture goes blank:

PSU: VS and VA voltages
Y-Sus: VSC (I can't see on board in the pic, but it's most likely the capacitor I've marked) and -Vy (test point is labeled -Vy TP)
Z-Sus: Zbias (aka Vzb)

Where your voltage test points are a cap or resistor (example: VSC and Zbias), place your negative probe on one lead of the cap or resistor and place your positive probe on the other lead.

[mh321]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

Here are my findings:
VSworking: 197.7 VSblank: 87
VAworking: 60.9 VAblank: 60.8
VSCworking: 199 VSCblank: 199
-VYworking: 25 -VYblank: 12.6
VZBworking: 95 VZBblank: 78

So once VS stops giving out 197V, the picture disappears on the TV.
Thanks

[capkid]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

The -Vy doesn't appear to have been measured correctly - it's extremely low and not shown as negative. I can't remember if this TV will you allow you to do it and continue to run, but you might want to try disconnecting the Y-Sus and Z-Sus from the PSU to see if the VS stays up.

[mh321]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

I think I measured it right this time:
-VYworking: 199.7 -VYblank: 199.6

I tried disconnecting the boards, but the VS keeps cycling from 0V to 197V about every 5 seconds.

[capkid]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

It does seem like the VS tract on the PSU has a failing component. However, the thing that makes me hesitant to declare that your PSU is bad is that you're able to unplug it for 10 secs then plug it back in and have the picture return.

[capkid]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

It does seem like the VS tract on the PSU has a failing component. However, the thing that makes me hesitant to declare that your PSU is bad is that you're able to unplug it for 10 secs then plug it back in and have the picture return.

[mh321]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

Is there anything else I can do or check to find out for sure what is wrong?

Thanks

[mh321]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

Any ideas anyone?

[capkid]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

You could try using a hair dryer and cold spray combination to see if you can reproduce the issue on command. I'm starting to wonder if your main board has a fault, so if you do try a hair dryer and cold spray, I wouldn't just focus on the PSU or Y-Sus.

[mh321]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

Is the cold spray the same thing as an electronics duster sprayed with the can upside down?
Thanks

[mh321]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

Also, does anyone know of a service manual for this TV?

[tom66]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

Yes you can reverse compressed air for freeze spray.
Service manual not for this TV but in my signature there's a link to service manuals, and there's documentation for the PDP50X3 panel used in your TV (I think.)

[mh321]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

I got the compressed air now yesterday. So I just use quick 0.5 second bursts on all components one by one? Can the ice that this spray makes conduct electricity?

[mh321]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

I tried the cold spray and hair dryer method and it has no effect on when the picture goes out. I cannot make the picture reappear or make the picture go out using cold or heat. Is there anything else I can try or measure?
Thanks

[mh321]

Re: HP Plasma CPTOH-0603- Picture goes blank after a few minutes

Is the power supply board probably bad?